Tokyo – A small amount of radioactive substances was found from urine samples of all of 10 children in Fukushima surveyed by a Japanese civic association and a French nongovernmental organization, the groups said Thursday.

David Boilley, president of the Acro radioactivity measuring body, told a news conference in Tokyo that the survey on 10 boys and girls aged between 6 and 16 in Fukushima city suggested there was a high possibility that children in and near the city had been exposed to radiation internally, Kyodo News reported.

The highest levels found by the survey were 1.13 becquerels of radioactive cesium-134 per 1 litre of urine from an 8-year-old girl, and 1.30 becquerels of cesium-137 in a 7-year-old boy, Kyodo said.

The city is located 60 kilometres north-west of the Fukushima Daiichi nuclear power station, which has been leaking radiaoactive material into the environment since it was hit by the March 11 earthquake and tsunami.

The radiation levels detected did not represent an immediate risk to health, but those two isotopes of cesium have half-lives of two and 30 years respectively, raising concerns about the long-term contamination of the environment and locally grown foodstuffs.

The Fukushima Network for Saving Children from Radiation, consisting of local parents, said the group would urge the central and local governments to have all citizens in the prefecture undergo detailed tests soon.

Acro previously investigated radiation exposure of children who lived near the site of the 1986 Chernobyl nuclear disaster in Ukraine.

Meanwhile, Tokyo Electric Power Co (TEPCO), which runs the plant, started its work Thursday to transfer low-level radiation-tainted water to a large floating container, which has a capacity to collect about 10,000 tons of water.

TEPCO said some 8,000 tons of water that the operator has stored at a temporary tank would be moved to the container, which is berthed along the quay near the plant, Kyodo reported.

The water came from the turbine buildings of reactors 5 and 6, and most of the water was believed to be seawater left after devastating tsunami waves hit the plant on March 11.

TEPCO has struggled to deal with 110,000 tons of contaminated water at the plant while a newly-installed water-treatment system has halted several times due to water leaks and other technical problems.